Engine bearing assemblies, such as crankshaft main bearings and connecting rod bearings, commonly comprise a pair of lined housings holding a rotatable shaft, with each housing being lined with a bearing shell. Each housing has a generally semi-cylindrical recess, shaped to receive a hollow generally semi-cylindrical bearing shell. The bearing shell typically comprises a backing layer that is provided with one or more layers on its concave inner surface, the innermost layer providing a running surface that faces the rotatable shaft.
The bearing shells in each bearing assembly may differ (e.g. having different materials or features), in which case it is preferred to ensure that the correct bearing shell is assembled into each of the housings (i.e. into the correct half of the bearing assembly). Alternatively, or additionally, bearing shells may be asymmetric along their circumference (for example if they are optimised for a particular direction of rotation of the shaft), in which case it is necessary to ensure that the bearing shells are assembled into the housing with the correct orientation. To ensure correct assembly of bearing shells into bearing housings, a bearing shell may be provided with an alignment feature, which projects outwardly from the convex outer surface of the bearing shell. The housing is provided with a corresponding alignment recess that receives the projecting alignment feature of the bearing shell.
FIGS. 1A and 1B illustrate a bearing shell 100 having a first type of alignment feature 102, which is manufactured by a first process, in which a narrow strip of material is pushed outwards (i.e. by being radially punched), with respect to the centre of curvature of the outer surface 104 of the bearing shell, into a die. The alignment feature 102 has parallel sides 106 parallel to the axial sides 108 of the bearing shell 100 (i.e. having constant axial width W, axial width being measured parallel with the axis of rotation of a shaft received into the bearing shell, and perpendicular to axial sides 108). The extent by which the alignment feature 102 projects from the convex outer surface of the bearing shell 100 tapers from a maximum projection level with the end face 110. For example, in the case that the bearing shell is approximately 20 mm wide (in the axial direction), and has a diameter of 60 mm, the alignment feature may be 3 mm wide, may project 1 to 2 mm from the convex outer surface of the bearing shell, and may extend approximately 5 mm around the circumference from the end face.
The alignment feature 102 in FIGS. 1A and 1B is shown closer to one axial side 108 than the other. However, it will be appreciated that the position of the alignment feature may be selected according to the individual requirements, and in some cases may be located equidistantly between the axial sides 108.
A second type of alignment feature is formed by a ‘coining’ process in which a punch is driven down onto an axially narrow, outer portion of an end face, which causes flow (i.e. deformation) of the punched material. Material flows out into a corresponding recess in a coining die supporting the bearing shell, and creates an alignment feature having the shape of a broad (i.e. along the axis of the bearing shell), outwardly projecting lip, that is slightly spaced apart from the end face. Any corresponding projection from the internal surface of the bearing shell should be avoided. An alignment feature of this second type, and a corresponding method of manufacture, is described in US2012027328A.
An alignment feature of either the first or second types provides a clear indication of the intended orientation of the bearing shell during assembly into a bearing housing (e.g. providing a visual indication to a worker during manual assembly, or providing a detectable indication of orientation during automated assembly), which provides a physical impediment to incorrect assembly. However, disadvantageously, such an alignment feature requires accurate axial alignment between the bearing shell and the bearing housing during assembly, which increases the complexity of assembly, and in particular reduces the reliability of automated assembly.